In recent years, there have been proposed and developed various variable valve timing control apparatus in which an angular phase of a camshaft relative to a timing sprocket, configured to rotate in synchronism with rotation of an engine crankshaft, is changed by transmitting rotary motion (torque) of an electric motor, through a speed reducer (in other words, a torque multiplier) to the camshaft, so as to variably control engine valve characteristics, such as valve closure timing and valve open timing of an engine valve (intake and/or exhaust valves).
One such electric-motor-driven phase-converter equipped variable valve timing control (VTC) apparatus has been disclosed in Japanese Patent Provisional Publication No. 2011-256798 (hereinafter is referred to as “JP2011-256798”). In the VTC apparatus disclosed in JP2011-256798, the output shaft of the electric motor is formed into a cylindrical-hollow shape, and bearing parts, such as a ball bearing and a needle bearing, are placed in the cylindrical-hollow motor output shaft. This machine-bearings layout contributes to the reduced entire axial length of the VTC apparatus, that is, the small-size VTC apparatus. Furthermore, bearing lubrication is made by supplying lubricating oil to the internal space of the cylindrical-hollow motor output shaft.
Also, electricity-feeding to the electric motor is achieved by sliding-contact of brushes, installed in a cover member configured to cover the front end of the electric motor of the phase converter, with respective slip rings of the electric-motor side. Hence, a plug is press-fitted into the front opening end of the cylindrical-hollow motor output shaft for preventing lubricating oil in the cylindrical-hollow motor output shaft from flowing toward and adhering to the brushes and slip rings.